Reciprocating-piston internal combustion engines, which will hereinafter also be referred to in shortened form merely as internal combustion engines, have one or more cylinders in which in each case one reciprocating piston is arranged. To illustrate the principle of a reciprocating-piston internal combustion engine, reference will be made below to FIG. 1, which illustrates by way of example a cylinder of an internal combustion engine, which is possibly also a multi-cylinder internal combustion engine, together with the most important functional units.
The respective reciprocating piston 6 is arranged in linearly movable fashion in the respective cylinder 2 and, together with the cylinder 2, encloses a combustion chamber 3. The respective reciprocating piston 6 is connected by means of a so-called connecting rod 7 to a respective crankpin 8 of a crankshaft 9, wherein the crankpin 8 is arranged eccentrically with respect to the crankshaft axis of rotation 9a. As a result of the combustion of a fuel-air mixture in the combustion chamber 3, the reciprocating piston 6 is driven linearly “downward”. The translational stroke movement of the reciprocating piston 6 is transferred by means of the connecting rod 7 and crankpin 8 to the crankshaft 9 and is converted into a rotational movement of the crankshaft 9, which causes the reciprocating piston 6, after it passes through a bottom dead center in the cylinder 2, to be moved “upward” again in the opposite direction as far as a top dead center. To permit continuous operation of the internal combustion engine 1, during a so-called working cycle of a cylinder 2, it is necessary firstly for the combustion chamber 3 to be filled with the fuel-air mixture, for the fuel-air mixture to be compressed in the combustion chamber 3 and to then be ignited and burned in an expanding fashion in order to drive the reciprocating piston 6, and finally for the exhaust gas that remains after the combustion to be discharged from the combustion chamber 3. Continuous repetition of this sequence results in continuous operation of the internal combustion engine 1, with work being output in a manner proportional to the combustion energy.
Depending on the engine concept, a working cycle of the cylinder 2 is divided into two strokes distributed over one crankshaft rotation)(360°) (two-stroke engine) or into four strokes distributed over two crankshaft rotations)(720°) (four-stroke engine). To date, the four-stroke engine has become established as a drive for motor vehicles. In an intake stroke, with a downward movement of the reciprocating piston 6, fuel-air mixture or else only fresh air (in the case of fuel direct injection) is introduced from the air intake tract 20 into the combustion chamber 3. During the following compression stroke, with an upward movement of the reciprocating piston 6, the fuel-air mixture or the fresh air is compressed in the combustion chamber 3, and if appropriate fuel is separately injected by means of an injection valve 5, which belongs to a fuel supply system, directly into the combustion chamber 3. During the following working stroke, the fuel-air mixture is ignited by means of an ignition plug 4, burned with an expanding action and expanded, outputting work, with a downward movement of the reciprocating piston 6. Finally, in an exhaust stroke, with another upward movement of the reciprocating piston 6, the remaining exhaust gas is discharged out of the combustion chamber 3 into the exhaust-gas outlet tract 30.
The delimitation of the combustion chamber 3 with respect to the air intake tract 20 or exhaust-gas outlet tract 30 of the internal combustion engine is realized generally, and in particular in the example taken as a basis here, by means of inlet valves 22 and outlet valves 32. In the current prior art, said valves are actuated by means of at least one camshaft. The example shown has an inlet camshaft 23 for actuating the inlet valves 22 and has an outlet camshaft 33 for actuating the outlet valves 32. There are normally yet further mechanical components (not illustrated here) for force transmission provided between the valves and the respective camshaft, which components may also include a valve play compensation means (e.g. bucket tappet, rocker lever, finger-type rocker, tappet rod, hydraulic tappet etc.).
The inlet camshaft 23 and the outlet camshaft 33 are driven by means of the internal combustion engine 1 itself. For this purpose, the inlet camshaft 23 and the outlet camshaft 33 are coupled in each case by means of suitable inlet camshaft control adapters 24 and outlet camshaft control adapters 34, such as for example toothed gears, sprockets or belt pulleys using a control mechanism 40, which has for example a toothed gear mechanism, a control chain or a toothed control belt, in a predefined position with respect to one another and with respect to the crankshaft 9 by means of a corresponding crankshaft control adapter 10, which is correspondingly embodied as a toothed gear, sprocket or belt pulley, to the crankshaft 9. By means of this connection, the rotational position of the inlet camshaft 23 and of the outlet camshaft 33 in relation to the rotational position of the crankshaft 9 is, in principle, defined. By way of example, FIG. 1 illustrates the coupling between inlet camshaft 23 and the outlet camshaft 33 and the crankshaft 9 by means of belt pulleys and a toothed control belt.
The rotational angle covered by the crankshaft during one working cycle will hereinafter be referred to as working phase or simply as phase. A rotational angle covered by the crankshaft within one working phase is accordingly referred to as phase angle. The respectively current crankshaft phase angle of the crankshaft 9 can be detected continuously by means of a position encoder 43 connected to the crankshaft 9, or to the crankshaft control adapter 10, and an associated crankshaft position sensor 41. Here, the position encoder may be formed for example as a toothed gear with a multiplicity of teeth arranged so as to be distributed equidistantly over the circumference, wherein the number of individual teeth determines the resolution of the crankshaft phase angle signal.
It is likewise additionally possible, if appropriate, for the present phase angles of the inlet camshaft 23 and of the outlet camshaft 33 to be detected continuously by means of corresponding position encoders 43 and associated camshaft position sensors 42. Since, owing to the predefined mechanical coupling, the respective crankpin 8, and with the latter the reciprocating piston 6, the inlet camshaft 23, and with the latter the respective inlet valve 22, and the outlet camshaft 33, and with the latter the respective outlet valve 32, move in a predefined relationship with respect to one another and in a manner dependent on the crankshaft rotation, said functional components run through the respective working phase synchronously with respect to the crankshaft. The respective rotational positions and stroke positions of reciprocating piston 6, inlet valves 22 and outlet valves 32 can thus, taking into consideration the respective transmission ratios, be set in relation to the crankshaft phase angle of the crankshaft 9 predefined by the crankshaft position sensor 41. In an ideal internal combustion engine, it is thus possible for every particular crankshaft phase angle to be assigned a particular crankpin angle HZW (FIG. 2), a particular piston stroke, a particular inlet camshaft angle and thus a particular inlet valve stroke and also a particular outlet camshaft angle and thus a particular outlet valve stroke. That is to say, all of the stated components are, or move, in phase with the rotating crankshaft 9.
In modern internal combustion engines 1, it is however possible for additional positioning elements to be provided within the mechanical coupling path between crankshaft 9 and inlet camshaft 23 and the outlet camshaft 33, for example in a manner integrated into the inlet camshaft adapter 24 and the outlet camshaft adapter 34, which positioning elements effect a desired controllable phase shift between the crankshaft 9 and inlet camshaft 23 and the outlet camshaft 33. These are known as so-called phase adjusters in so-called variable valve drives. Also symbolically illustrated is an electronic, programmable engine control unit 50 (CPU), which is equipped with signal inputs for receiving the various sensor signals and with signal and power outputs for actuating corresponding positioning units and actuators for controlling the engine functions.
For optimum operation of the internal combustion engine (with regard to emissions, consumption, power, running smoothness etc.), the fresh-gas charge introduced into the combustion chamber during the intake stroke should be known to the best possible extent in order to enable the further parameters for the combustion, such as for example the fuel quantity which is to be supplied, and which is possibly directly injected, to be coordinated therewith. The so-called charge exchange, that is to say the intake of fresh gas and the discharge of the exhaust gas, is in this case highly dependent on the control timing of the inlet valves 22 and outlet valves 32, that is to say on the profile with respect to time of the respective valve strokes in relation to the profile with respect to time of the piston stroke. In other words, during operation, the charge exchange is dependent on the phase positions of the inlet and outlet valves in relation to the crankshaft phase angle and thus in relation to the phase position of the reciprocating piston.
The prior art for acquiring the fresh-gas charge and for coordinating the control parameters of the internal combustion engine therewith comprises measuring a so-called reference internal combustion engine in all occurring operating states, for example as a function of the rotational speed, the load, if appropriate of the valve control timings predefinable by means of phase adjusters, if appropriate the operating parameters of exhaust-gas turbocharger or supercharger etc., and storing these measurement values or derivatives thereof or model approaches representing the behavior on the engine control unit of a corresponding series-production internal combustion engine. All structurally identical, series-produced internal combustion engines of the same type series are then operated with this reference dataset that is generated.
A deviation, resulting for example from manufacturing tolerances, of the actual relative positions between inlet valves and outlet valves and the crankshaft phase angle or the reciprocating-piston position of a series-production internal combustion engine in relation to the ideal reference positions of the reference internal combustion engine, that is to say a phase difference of the inlet valve stroke, of the outlet valve stroke and if appropriate of the piston stroke in relation to the crankshaft phase angle predefined by the crankshaft position sensor, or the phase position of the crankshaft, has the effect that the fresh-gas charge actually drawn in deviates from the fresh-gas charge determined as a reference, and thus the control parameters based on the reference dataset are not optimum. During the operation of the internal combustion engine, these errors can have adverse effects with regard to emissions, consumption, power, running smoothness etc.
For the illustration of the possible deviations that occur in a series-production internal combustion engine, and for the definition of the nomenclature of said deviations, reference will be made below to FIG. 2, which shows the internal combustion engine from FIG. 1 but in which, for a better overview, the reference designations illustrated in FIG. 1 have been omitted and only the corresponding deviations are designated.
Proceeding from a reference position of the position encoder 43 arranged on the crankshaft control adapter 10, the phase angle of which position encoder is detected by the crankshaft position sensor 41, there are resulting multiple tolerance chains that lead to deviations of the phase positions, hereinafter also referred to as phase differences, of reciprocating pistons 6, inlet valves 22 and outlet valves 32 in relation to the ideal reference phase positions. Here, the piston stroke phase difference ΔKH results for example from a deviation of the crankpin angle HZW, the so-called crankpin angle difference ΔHZW, in relation to the reference position of the crankshaft position sensor 41 and from different dimensional tolerances (not illustrated) of connecting rod 7 and reciprocating piston 6.
Furthermore, the inlet valve stroke phase difference ΔEVH results for example from a deviation in the cam position, the so-called inlet camshaft angle difference ΔENW, together with mechanical tolerances (not illustrated) of the inlet camshaft control adapter 24 and of the control mechanism 40. If a phase adjuster for the inlet camshaft is present, then consideration is possibly also given to an inlet camshaft adjustment angle ENVW or to a deviation thereof from the setpoint. In the same way, the outlet valve stroke phase difference ΔAVH results for example from a deviation in the cam position, the so-called outlet camshaft angle difference ΔANW, together with mechanical tolerances (not illustrated) of the outlet camshaft control adapter 24 and of the control mechanism 40. If a phase adjuster for the outlet camshaft is present, then consideration is possibly also given to an outlet camshaft adjustment angle ANVW or to a deviation thereof from the setpoint.
Possible causes of the described deviations may for example be:
manufacturing and/or assembly tolerances of the mechanical components involved, and
wear phenomena, such as for example a lengthening of the control chain or of the toothed belt by means of which the crankshaft and the camshafts are coupled, and
deformation phenomena, elastic or plastic, resulting from high mechanical load states.
The previous solution to the described problem as per the current prior art lies, in principle, in detecting and quantifying the occurring deviations between reference internal combustion engine and series-production internal combustion engine in order to be able to implement corresponding measures for correction or compensation through adaptation of control parameters. Furthermore, it has hitherto been sought to counteract this problem by minimizing manufacturing and assembly tolerances. Furthermore, for example, the control timings are measured on the respective static series-production internal combustion engine on the basis of valve stroke position, cam contour etc., and the internal combustion engine is correspondingly adjusted during the assembly process.
Furthermore, most presently known systems operate with a reference point system (position feedback). Here, in each case one position mark that can be detected by means of a sensor is placed on the crankshaft and on the inlet camshaft and/or on the outlet camshaft, or also on the respective crankshaft control adapter and on the inlet camshaft control adapter and/or on the outlet camshaft control adapter, or also on a phase adjuster that may be provided, etc. In this way, the relative phase position between the crankshaft and the respective inlet camshaft and/or outlet camshaft can be acquired, and deviations in relation to the desired reference values can be identified. The undesired effects of said deviations can then be counteracted in the control unit by means of an adaptation or correction of corresponding control parameters in a manner dependent on the acquired deviations.
In principle, however, only some of the occurring tolerances can be identified by means of this method. For example, it is thus not possible to identify an angular deviation owing to a position deviation of the respective position marks themselves in relation to the camshafts, or an inlet camshaft angle difference ΔENW or an outlet camshaft angle difference ΔANW in relation to the respective reference position. Further methods, such as evaluating the knock sensor signal, evaluating the cylinder pressure signal, are likewise known. For example, U.S. Pat. No. 6,804,997 B1 has disclosed an engine control device for determining the phase position of the crankshaft by monitoring and evaluating pressure fluctuations of the intake air in the air intake tract. The control device is designed so as to determine intake air pressure fluctuations, which indicate an intake air event, and thus a crankshaft phase position related thereto and the corresponding period thereof of the engine cycle. The control device utilizes these items of information to acquire the crankshaft rotational speed and the phase position of the crankshaft in order to control the fuel injection and the ignition characteristics of the engine. The control timings of the inlet valves and outlet valves, that is to say if appropriate the inlet valve stroke phase differences and outlet valve stroke phase differences, are not taken into consideration in this case, and can under some circumstances considerably influence the result.
DE 10 2005 007 057 discloses a closed-loop control method for a throttle flap air stream, which is to be controlled in closed-loop fashion, in the intake tract of an internal combustion engine, wherein pressure pulsations of the intake air in the air intake tract, which are also influenced inter alia by the valve control timings of the internal combustion engine, are taken into consideration in the closed-loop control of the fluid stream. For this purpose, the pressure pulsations are analyzed by means of fast Fourier transformation, and the amplitude information is summarized in a distortion factor which is taken into consideration as an additional input variable for example for a multi-dimensional mathematical closed-loop control model of the throttle flap air stream. Specific conclusions regarding the valve control timings, that is to say also possibly present inlet valve stroke phase differences and outlet valve stroke phase differences, of the internal combustion engine cannot be drawn by means of this method.
DE 35 06 114 A1 discloses a method for the open-loop or closed-loop control of an internal combustion engine in which, in a manner dependent on an operating variable which comprises at least a part of an oscillation spectrum of the internal combustion engine as information, such as for example gas pressure signals, at least one manipulated variable of the internal combustion engine is controlled. For this purpose, the value spectrum contained in the detected operating variable is determined therefrom, as a part of the oscillation spectrum, by discrete Fourier transformation and is used as a measurement spectrum and compared with a reference spectrum. The manipulated variable of the internal combustion engine which is to be controlled is then controlled as a function of the deviation between the measurement spectrum and the reference spectrum. A specific conclusion regarding the valve control timings and piston stroke position of the internal combustion engine cannot be easily drawn by means of this method either.
US 2009 0 312 932 A1 discloses a method for performing diagnostics on the combustion within an internal combustion engine, wherein a combustion phase setting value is generated from the crankshaft angular speed by means of a fast Fourier transformation, said value is compared with an expected combustion phase setting value, and differences between said values greater than an admissible combustion phase setting difference are identified. A similar approach for determining deviations between a reference engine and series-production engine to those described above is also disclosed in US 2010 0 063 775 A1.